This 2D side-view companion to the 3D marble run lets you watch the physics instead of just the spectacle: a marble drops down a ramp, threads a full loop-the-loop, zigzags through a narrowing funnel chute and coasts to a stop on a flat run-out, all driven by real rolling-sphere dynamics. Track tilt sets how much gravitational potential energy the marble starts with, the friction slider controls how much of that energy the rails bleed off per meter, and marble mass changes how kinetic energy and momentum scale even though — as the readouts reveal — a heavier or lighter marble reaches the bottom of a given track at exactly the same speed. Watch the normal-force readout spike as the marble crosses the top of the loop, where the rails must supply the centripetal force needed to keep it curving, then ease back to a simple gravity-times-cosine value on the straight run-out.